Aequorin is a protein of low molecular weight isolated from the jellyfish Aequorea forskalea. Aeauorin bioluminesces blue in the presence of Ca++ ions, and this property has made the protein a valuable tool for the study of Ca++ transients in biological cells. From the biochemical standpoint the protein is unusual in that it requires no exogenous cofactors such as ATP, luciferin, or exogenous molecular oxygen for its bioluminescence (cg bioluminescent systems from firely, earthworms or the sea pansy, (renilla). Rather, it appears that all the reqired cofactors are entrapped inthe native protein. Aequorin is therefore analogous to an enzyme trapped in a transition state and we may surmise that Ca++ acts to rigger conformational changes in the protein which result in oxcidation of an intrinsic chromophore. The response to Ca++ is truly catalytic in the sense that Ca++ enhances rate of reaction,but theprotein is not an enzyme in that it can "turn-over" only once when Ca++ binds. However, the physiococohemical factors that influence sthe binding of Ca++, the nature of conformation changes induced in the protein by ion binding, the amino acid sequence and the secondary and tertiary structuresof the protein, the nature of the binding and "active" sites, the state o the bound chromophore, the identity of amino acid side chains that promote catalysis of oxidation of the chromophore and the basic mechanisms that underlie bioluminescence are all unknown. We will determine the amino acid sequence of the protein, utilize standard spectroscopic techniques to deterine secondary and tertiary structure of the protein, and use a variety of biochemical and biophysical techniques toward elucidation of the factors that govern ion binding, the nature of conformational changes andthe nature of the chemical reactions in the protein that result in bioluminescence. We hope the data will allow us to infer the mechanisms that underlie the bioluminescent process.